The field of the present invention pertains to processes and apparatus related to chemical mechanical polishing operations for fabricating semiconductors and integrated circuits. More particularly, the present invention relates to the field of dispensing slurry on a polish pad and for conditioning a polish pad for chemical mechanical polishing operations.
Conventional integrated circuits (IC) are fashioned from miniature electrical devices such as resistors, diodes, and transistors. These miniature electrical devices are created by using deposition operations to create layers of material, by using photolithography to create patterns in the wafer, and by using chemical mechanical polishing (CMP) operations to polish away unwanted portions of the layers of material. In order to provide consistent and even layers, a need arises for a method and apparatus that can polish a wafer surface to be very flat.
CMP is the preferred method for planarizing a semiconductor wafer. In particular, CMP flattens out height differences between high spots and low spots on the wafer. This is accomplished via mechanical contact between the wafer and a moving polish pad that is saturated with an abrasive polish slurry. Polishing in this manner is the only technique that provides a smooth topography when examined on a millimeter scale. That is, the wafer is essentially flat when measured over the distance of a millimeter.
Prior art FIG. 1A is a plan view of a chemical mechanical polishing (CMP) machine 100. Prior art FIG. 1B is an elevation view of CMP machine 100. CMP machine 100 picks up a wafer to be polished with a carrier arm 101 and holds it against a rotating polish pad 102. Polish pad 102 is made of a resilient material and is textured, often with multiple predetermined grooves 103, to aid the polishing process. Polish pad 102 rotates on a platen, or turntable, 104 located beneath polish pad 102, at a predetermined speed. A wafer 105 is held in place on polish pad 102 within a carrier ring 112 that is connected to a carrier 106 of carrier arm 101. The front surface of wafer 105 rests against polish pad 102. The back surface of wafer 105 is held against a surface of carrier 106 of carrier arm 101. As polish pad 102 rotates in one direction 114, e.g. a clockwise direction 114, carrier 106 itself rotates wafer 105 at a predetermined rate. CMP machine 100 also includes a slurry dispense arm 107 extending across the radius of polish pad 102. Slurry dispense arm 107 dispenses a flow of polish slurry onto polish pad 102 via port 132. To improve dispersal of polish slurry over polish pad 102, slurry dispense arm 107 disperses polish slurry while it traverses across the radius of polish pad 102 in direction 134.
To aid in maintaining a stable removal rate, CMP machine 100 includes a conditioner assembly 120. Conditioner assembly 120 includes a conditioner arm 108, which extends across the radius of polish pad 102. An end effector 109 is connected to conditioner arm 108. End effector 109 includes an abrasive conditioning disk 110 that is used to roughen the surface of polish pad 102. Conditioning disk 110 is rotated by conditioner arm 108 in the same direction as pad 102, e.g. in a clockwise direction 130, and is transitionally moved across the radius of polish pad 102 in direction 138, such that conditioning disk 110 covers the radius of polish pad 102. In so doing, conditioning disk 110 covers the surface area of polish pad 102, as polish pad 102 rotates. The pad is conditioned by conditioning assembly 120 to help keep the pad profile as flat as possible. However, there is no guarantee that conditioner assembly 120 actually conditions the polish pad 102 precisely where the wafer contacted the polish pad. If there is a mismatch between the polishing operation, where wafer 105 contacted polish pad 102, and the conditioning operation, where conditioning disk 110 contacts polish pad 102, then the pad profile may become skewed. Similarly, if conditioning assembly 120 is biased to a region, it may result in uneven polishing because of the uneven conditioning of polish pad 102. Furthermore, conditioning assembly 120 can be a source of defect particles. Consequently, a need arises for a method of conditioning a pad that will ensure a consistent and flat pad profile.
A polish pad with a roughened surface has an increased number of micro-pits and gouges in its surface that produces a faster removal rate of material from wafer 105 via increased slurry transfer to the surface of wafer 105. The surface texture of the polish pad is created from conditioner assembly 120, which is typically coated with diamonds. Without conditioning, the surface of polish pad 102 is smoothed during the polishing process and removal rate decreases dramatically. Conditioner assembly 120 re-roughens the surface of polish pad 102, thereby keeping the grooves cleaned out, improving the transport of slurry, and improving the removal rate of material from the wafer.
As described above, the CMP process uses abrasive slurry on a polish pad. The polishing action of the slurry is comprised of an abrasive frictional component and a chemical component. The abrasive frictional component is due to the friction between the surface of the polish pad, the surface of the wafer, and the abrasive particles suspended in the slurry. The chemical component is due to the presence in the slurry of polishing agents that chemically interact with the material of the dielectric layer of wafer 105. The chemical component of the slurry is used to soften the surface of the dielectric layer to be polished, while the frictional component removes material from the surface of wafer 105.
As shown by prior art FIGS. 1A and 1B, the conventional method of dispensing slurry onto the polish pad uses a separate dedicated device, e.g. slurry dispense arm 107, that has a control mechanism for moving across the pad to deliver polish slurry across the entire radius of polish pad 102. This conventional method and apparatus proliferates the control mechanisms, and the complexity of the CMP machine. Consequently, a need arises for an apparatus and method of reducing the complexity of a slurry dispense mechanism for the polishing operation.
Conventional controls attempt to align slurry dispense arm 107 with the anticipated location of the wafer being polished. However, there is no guarantee that slurry dispense arm 107 will provide slurry material precisely where the wafer will contacted the polish pad. If there is a mismatch between the location of the slurry deposited on polish pad 102, and the location of the wafer contacting polish pad 102, nearly 270xc2x0 later, then the pad profile and the polishing rate across wafer 105 may become uneven. Consequently, a collateral need arises in the CMP operation is to improve the uniformity of polish slurry dispensing.
Similarly, as shown by prior art FIGS. 1A and 1B, the conventional method of conditioning the polish pad uses a separate dedicated device, e.g. conditioner assembly 120, that has a control mechanism for circular motion and for rotational motion across the polish pad. This conventional method and apparatus proliferates the control mechanisms and the size of a CMP machine. Consequently, a need arises for an apparatus and method of reducing the complexity of a conditioning mechanism for the polishing operation. A collateral need in the CMP operation is to improve the efficiency of pad conditioning.
In summary, a need arises for a method and apparatus that can create a very flat surface on the wafer. More specifically, a need arises for an apparatus and method of reducing the complexity of a slurry dispense mechanism for a CMP polishing operation. A collateral need arises in the CMP operation to improve the uniformity of polish slurry dispensing. Yet another need arises for an apparatus and method of reducing the complexity of a conditioning mechanism for the polishing operation. A collateral need arises in the CMP operation is to improve the efficiency of pad conditioning.
The present invention provides a method and apparatus of point of polish slurry dispensing. The present invention also improves the uniformity of polish slurry dispensing Hence, the present invention is able to create a very flat surface on a wafer being polished. Furthermore, the present invention provides an apparatus and method with reduced complexity for dispensing polish slurry for a CMP polishing operation.
The present invention also provides a method and apparatus of point of polish conditioning. The present invention also provides a method of conditioning a pad that will ensure a flat pad profile. Additionally the present invention provides an apparatus and method with reduced complexity for conditioning in a polishing operation. Additionally, the present invention provides more efficient pad conditioning.
One embodiment of the present invention provides a chemical mechanical polishing (CMP) machine for performing a CMP operation on a wafer. The CMP machine includes a polish pad, a carrier arm, and a carrier ring. The carrier ring, which is coupled to the carrier arm, has a slurry dispensing port on a bottom face of the carrier ring, which is adapted to interface with the top surface of the polish pad. By incorporating the slurry dispensing function into the carrier ring, the present invention takes advantage of the existing translational motion of the carrier ring across the polish pad. Furthermore, point of polish pad slurry dispensing ensures that slurry is dispensed in locations where the wafer will contact with the pad because the dispensing mechanism is proximately located around the wafer itself. Thus, the present invention eliminates the possibility of polishing a wafer on a portion of the pad that inadequate slurry. This helps ensure an even polishing and improved wafer flatness.
Similarly, the carrier ring has a conditioning device on a bottom face of the carrier ring. By incorporating the conditioning device function into the carrier ring, the present invention takes advantage of the existing rotational motion and translational motion of the carrier ring. Consequently, the present invention eliminates the requirement for a separate conditioning device that has both rotational motion and translational motion. Thus the present invention provides a CMP machine with a conditioning device and a slurry dispensing at the point of polish without the added complexity and other limitations associated with the conventional CMP operation. This embodiment is referred to as point of polish pad slurry dispensing and point of polish pad conditioning because the operations occur proximate to the actual wafer being polished.
Another embodiment of the present invention provides a flowchart implementation of the improved CMP process. In the first step, polish slurry is received at the CMP machine. In a second step, the polish pad is rotated. Next, polish slurry is dispensed proximately around the wafer being polished. That is, the polish slurry is dispensed through the carrier ring that holds the wafer. Thus, the polish slurry is provided at the spatial point of polish of the wafer. In a subsequent step, the polish pad is conditioned proximately around the wafer being polished. The conditioning pins and the dispensing ports are interspersed around a carrier ring to provide consistent and efficient slurry dispensing and conditioning of the polish pad. This eliminates the prior art""s mismatch of locations at which the slurry is dispensed, the pad is conditioned, and the wafer is polished.
With an even dispensing of polish slurry around the carrier ring, the polish slurry that is discharged upstream of the wafer provides the polish medium to the wafer. In contrast, the polish slurry that is discharged downstream of the wafer acts as a medium to remove waste from the polishing of the wafer. That is, the polish slurry dispensed downstream of the wafer transports the polishing waste, occurring immediately upstream via the centrifugal force of the spinning polish pad. This process is continued until the degree of desired polishing is accomplished. This method is referred to as a point of polish pad dispensing and conditioning because the dispensing and the polishing occur at the proximate to the actual wafer being polished.
These and other advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the drawing figures.